The present invention relates to an internal latent image type direct positive photographic silver halide emulsion and a color diffusion transfer photographic light-sensitive material comprising such an internal latent image type direct positive photographic silver halide emulsion.
The silver halide system photography is superior to other photographic processes such as electrophotography and diazo process in sensitivity and gradation characteristics and thus has heretofore been most widely used. A known example of the silver halide system photography is a photographic process for the formation of a direct positive image. In this photography, an internal latent image type direct positive photographic silver halide emulsion is developed with a surface developer (developer which leaves the latent image forming position inside silver halide grains substantially undeveloped) while being uniformly exposed to light or in the presence of a nucleator as disclosed in U.S. Pat. No. 3,761,276 and JP-B-60-55821 (The term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d).
The direct positive photographic silver halide emulsion is superior to the negative type emulsion in that it may be processed only once to obtain a positive image.
In general, an internal latent image type direct positive photographic silver halide emulsion is prepared by a process which comprises mixing a soluble silver salt with a soluble halide in an aqueous solution of gelatin to form silver halide grains (hereinafter referred to as xe2x80x9ccore grainsxe2x80x9d), subjecting the core grains to chemical sensitization, depositing a silver halide on the core grains to form a shell thereon, desalting the emulsion, and then optionally subjecting the emulsion to chemical sensitization.
For example, JP-B-52-34213 (corresponding to U.S. Pat. No. 3,761,276) discloses an internal latent image type emulsion useful for a direct positive emulsion. This emulsion comprises silver halide grains which contains a doping agent inside and has been chemically sensitized on its surface. This is also disclosed in U.S. Pat. No. 3,317,322 to Porter et al.
The present invention relates to an emulsion of tabular silver halide grains. Processes for the preparation of such an emulsion of tabular silver halide grains and techniques using such an emulsion of tabular silver halide grains are disclosed in Cleve, xe2x80x9cPhotography: Theory and Practicexe2x80x9d, 1930, page 131, Gutoff, xe2x80x9cPhotographic Science and Engineeringxe2x80x9d, vol. 14, pp. 248-257, 1970, U.S. Pat. Nos. 4,434,226, 4,414,310, 4,433,048, 4,439,520, 4,414,306, 4,459,353, British Patent 2,112,157, JP-A-59-99433 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) and JP-A-62-209445. In particular, tabular internal latent image type direct positive photographic silver halide emulsions are described in detail in U.S. Pat. Nos. 4,395,478, 4,504,570 and 4,996,137, JP-B-64-8327, JP-A-1-131547, JP-A-1-154142, JP-A-1-158429 and JP-A-1-297649. These tabular internal latent image type direct positive photographic silver halide emulsions are advantageous in that they exhibit an excellent sharpness and undergo development rapidly to provide a direct positive image having a small dependence on development temperature.
However, the tabular internal latent image type direct positive photographic silver halide emulsions thus prepared are disadvantageous in that they can easily form a re-reversed negative image which frequently occurs when exposed to light at a high intensity.
As an approach for solving this problem to minimize the formation of re-reversed negative image there is taught in U.S. Pat. Nos. 3,367,778, 3,287,136 and 4,395,478 a method which comprises doping polyvalent metal ions into silver halide grains. However, this process cannot provide sufficient improvements when applied to tabular internal latent image type direct positive photographic silver halide emulsions.
It has thus been desired to develop a tabular internal latent image type direct positive photographic silver halide emulsion which can hardly form a re-reversed negative image while maintaining its excellent characteristics.
These emulsions leave something to be desired in stability in production.
For the method for the preparation of an emulsion of tabular grains, reference can be made to JP-A-58-113927, JP-A-58-113928, JP-A-58-127921 and JP-A-1-158426. However, these methods require a prolonged period of time to form grains and thus present a big productivity problem. Further, these methods leave something to be desired in scale dependence during the formation of grains and reproducibility. In particular, the preparation of tabular internal latent image type direct positive photographic silver halide emulsions is complicated and requires a prolonged period of time, showing a poor reproducibility.
On the other hand, as an approach for stabilizing the formation of grains there is known a so-called seed crystal method which comprises the growth of seed crystal grains which have been separately prepared. However, this method has never been applied to internal latent image type direct positive emulsions. Further, as a method for preparing tabular grains by seed crystal method there is disclosed in JP-B-3-46811 a grain formation method using spherical seed crystal grains (aspect ratio: 1). However, the grains obtained by this method have an aspect ratio of not more than 3.0. Thus, this method cannot provide grains having a high aspect ratio.
Moreover, JP-A-61-112142, JP-A-62-58237 and JP-A-55-142329 disclose a grain formation method using polytwin grains. This method is suitable for the preparation of tabular grains having a high aspect ratio. However, this method is disadvantageous in that the grains thus obtained are susceptible to variation of characteristics unless seed crystals which have been desalted and redispersed are allowed to grow rapidly. Thus, this method leaves something to be desired in stability in production.
Further, JP-A-3-196136 and JP-A-3-196137 disclose a technique which comprises the formation of grains in the presence of a silver oxidizing agent. However, this technique has never been applied to the preparation of seed crystal emulsions.
As mentioned above, the stability in the preparation of an internal latent image type direct positive photographic silver halide emulsion, particularly a tabular internal latent image type direct positive photographic silver halide emulsion, presents a big problem. Nevertheless, no good solutions have been found.
It is therefore an object of the present invention to provide a tabular internal latent image type direct positive photographic silver halide emulsion which exhibits a high sensitivity and is less susceptible to the formation of re-reversed negative image and a color diffusion transfer photographic light-sensitive material comprising such a tabular internal latent image type direct positive photographic silver halide emulsion.
It is another object of the present invention to provide an internal latent image type direct positive photographic silver halide emulsion (particularly tabular internal latent image type direct positive photographic silver halide emulsion) having an excellent production stability and a color diffusion transfer photographic light-sensitive material comprising such an internal latent image type direct positive photographic silver halide emulsion.
These and other objects of the present invention will become more apparent from the following detailed description and examples.
The first aspect of the present invention is an internal latent image type direct positive photographic silver halide emulsion comprising tabular silver halide grains having an average grain diameter of not less than 0.3 xcexcm and an aspect ratio (diameter of silver halide grain in circle equivalence/thickness of silver halide grain) of from not less than 2 to not more than 100 in an amount of not less than 50% of all silver halide grains as calculated in terms of area, wherein the average grain thickness a along the main plane of the external shell thereof is from not less than 0.2 xcexcm to not more than 1.5 xcexcm and the average grain thickness b perpendicular to the main plane of the external shell thereof is from not less than 0.04 xcexcm to not more than 0.30 xcexcm.
The second aspect of the present invention is the internal latent image type direct positive photographic silver halide emulsion as defined in the first aspect above, which is prepared from a seed crystal emulsion which has been prepared via desalting process.
The third aspect of the present invention is the internal latent image type direct positive photographic silver halide emulsion as defined in the first aspect above, wherein grains are subjected to chemical sensitization in the presence of at least one compound selected from the group consisting of compounds represented by the following formula (A), (B) or (C):
Rxe2x80x94SO2xe2x80x94Sxe2x80x94Mxe2x80x83xe2x80x83(A)
Rxe2x80x94SO2xe2x80x94Sxe2x80x94R1xe2x80x83xe2x80x83(B)
Rxe2x80x94SO2Sxe2x80x94(L)mxe2x80x94SSO2xe2x80x94R2xe2x80x83xe2x80x83(C)
wherein R, R1 and R2 may be the same or different and each represents an aliphatic group, aromatic group or heterocyclic group; M represents a cation; L represents a divalent linking group; m represents 0 or an integer of 1; the compounds of the formula (A), (B) or (C) may be each in the form of polymer containing as a repeating unit a divalent group derived from the structures represented by the formulae (A), (B) and (C), respectively; and R, R1, R2 and L may be optionally connected to each other to form a ring.
The fourth aspect of the present invention is the internal latent image type direct positive photographic silver halide emulsion as defined in the third aspect above, wherein the chemical sensitization of core grains is effected in the presence of at least one compound selected from the group consisting of the compounds represented by the formula (A), (B) or (C) and a gold sensitizer in combination under the condition that substantially no thiosulfate ion is present during the chemical sensitization.
The fifth aspect of the present invention is the internal latent image type direct positive photographic silver halide emulsion as defined in the third aspect above, wherein the silver halide phase of the external shell is formed in the presence of at least one compound selected from the group consisting of the compounds represented by the formula (A), (B) or (C).
The sixth aspect of the present invention is the internal latent image type direct positive photographic silver halide emulsion as defined in the third aspect above, which is prepared from a seed crystal emulsion which has been prepared via desalting process.
The seventh aspect of the present invention is the internal latent image type direct positive photographic silver halide emulsion as defined in the first aspect above, wherein the average grain thickness a along the main plane of the external shell thereof is from not less than 0.4 xcexcm to not more than 1.0 xcexcm and the average grain thickness b perpendicular to the main plane of the external shell thereof is from not less than 0.06 xcexcm to not more than 0.15 xcexcm.
The eighth aspect of the present invention is the internal latent image type direct positive photographic silver halide emulsion as defined in the first aspect above, wherein the thickness of grains are so uniform that the coefficient of variation of thickness is not more than 30%.
The ninth aspect of the present invention is a color diffusion transfer photographic light-sensitive material comprising at least one photosensitive silver halide emulsion layer combined with a dye image-forming substance provided on a support, said dye image-forming substance comprising a nondiffusive compound represented by the following formula (I) which releases a diffusive dye or precursor thereof or changes in its diffusivity in connection with silver development, wherein said at least one silver halide emulsion layer comprises at least one internal latent image type direct positive photographic silver halide emulsion as defined in the first aspect:
(DYExe2x88x92Y)nxe2x88x92Zxe2x80x83xe2x80x83(I)
wherein DYE represents a dye group or a dye group or dye precursor group whose absorption wavelength has been temporarily shifted to short wavelength; Y represents a mere bond or bridging group; Z represents a group which makes difference in the diffusivity of the compound represented by (DYExe2x88x92Y)nxe2x88x92Z or releases DYE to make difference in diffusivity between the released DYE and (DYExe2x88x92Y)nxe2x88x92Z in correspondence or counter correspondence to a photosensitive silver salt having an imagewise latent image; and n represents an integer of 1 or 2, with the proviso that when n is 2, the plurality of (DYExe2x88x92Y)""s may be the same or different.
The tenth aspect of the present invention is an internal latent image type direct positive photographic silver halide emulsion, prepared from a seed crystal emulsion which has been prepared via desalting process.